EXPRESSION OF THE MANNOPINE SYNTHASE PROMOTER IN ROOTS IS DEPENDENT ON THE MAS ELEMENTS AND CORRELATES WITH HIGH TRANSCRIPT LEVELS OF MAS-BINDING FACTOR

The expression of the bidirectional mannopine synthase 1'2' promoter of Agrobacterium tumefaciens was analyzed by transient expression in potato and tobacco protoplasts as well as in transgenic potato plants. The coding region of the beta-glucuronidase gene was fused to either side of the wild type promoter as well as to internal deletion constructs removing the mas elements, ocs-like sequences present at each transcription start site. Both mas elements were shown to be necessary for full activity by transient expression in potato and tobacco protoplasts. Transgenic plants harbouring wild type promoter-beta-glucuronidase gene fusions showed expression which was highest in roots and significantly lower in petioles and leaves. Tubers had hardly detectable levels of glucuronidase activity. The internal deletions of the mas elements significantly affected expression in roots but not in other tissues, indicating their importance for mas promoter activity in roots. The level of RNA coding for mas-binding factors, DNA-binding proteins that are able to bind to the mas elements, correlates with the expression pattern conferred by the mas1'2' promoter.